Remote vehicle starting systems currently available on the market utilize a portable hand-held transmitter that issue a binary coded sequence in the form of an RF transmission to signal a slave controller mounted oh board the vehicle to energize the starter motor in order to crank the engine. During the start-up sequence the controller constantly monitors the rotational speed of the engine. When the speed reaches or exceeds a certain threshold, in the range of 500 to 1000 revolutions per minute (RPM), the slave controller determines that the start-up sequence has been successful and de-energizes the starter motor.
A convenient way of- determining the speed of revolution of an internal spark-induced combustion engine is to monitor the electrical activity at the ignition coil. The voltage observed at the negative terminal of the coil varies dynamically and can be represented by a pulse train where each pulsation corresponds to a single cylinder ignition event. The crank shaft speed of revolution is function of the number of pulses per unit of time (alternatively, the crank shaft speed can be expressed as function of the elapsed time between two successive pulses) and the number of cylinders of the particular engine. The latter parameter determines the quantity of pulses generated during a single crank shaft revolution.
The on-board slave controller is a microprocessor operated unit adaptable to engines having different number of cylinders. This versatility is achieved by modifying the program processing the tachometer signal from the ignition coil. During the installation oft he system, the technician accesses the programming mode of the slave controller and loads in memory the basic parameters of the engine that is to be controlled, such as the number of cylinders and the speed that the engine must attain before the starter motor is de-energized, among others. This data provides the main program with the necessary parameters to factor the engine characteristics of the specific application in the various computations of the tachometer signal.
Remote starting system for diesel engines present a difficult challenge. The absence of electric ignition that provides a convenient tachometer signal requires a special sensor to monitor the speed of rotation of the engine. The prior art has developed a number of methods to measure the speed of rotation of a diesel engine. Examples of such methods include observing the pressure pulsations of diesel fuel in the injector lines, measuring the dynamic pressure variations in the crank case and sensing by magnetic proximity sensors the motion of rocker arms. Those methods, however, are unpractical for use in remote vehicle starting systems for the following reason for the following reason. Remote vehicle starting systems are rarely installed as original equipment by automobile manufacturers. The trend is to commercialize the systems as after market equipment. Hence, the systems are designed and built for universal application in order to fit many different automobiles. This requirement rules out the use of speed sensor arrangements that are application-specific. Otherwise, the large number of different diesel engines in commercial use would require from the manufacturer of the remote starting system to design and keep in stock a wide variety of speed sensors to suit all possible applications.